Classifying Rocks

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Vocabulary

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Texture: The look and feel of any rock's surface determined by the rock's size, shape, and pattern of a rock's grains.
Grains:A particle of a type of mineral or other rock that gives a kind of rock its texture.
Igneous Rocks: A type of rock that can form from cooling of hot, molten rock at or under the surface or top.
Sedimentary Rocks: A type of rock that can form when pieces from other rocks or the leftovers or remains of plants or animals are pressed together with pressure and cemented together.
Metamorphic Rocks: One type of rock that can form from a rock that is already there or existing that is changed by temperature, pressure, or some kinds of chemical reactions.

Outline

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How Geologists Classofy Rocks

• Rocks are very important building blocks for the earth and its moon.
  • Rocks on earth forms mountains and hills, valleys, beaches, and even the ocean floor
  • Earth's crust is made out of lots of types of rocks
    • Rocks are made of mixtures of minerals and other minerals, although sometimes, rocks may only contain one single type of mineral.
    • When studying any rock sample, all geologists observe the rock's color and the rock's texture and try to determine the mineral compostition of the rock.
      • Using all these characteristics of a rock, all geologists can calssify a rock.

Texture

• With minerals, color by itself does not provide enough imformation to identify a type of rock.
  • The texture of a rock is very useful in trying to identify a type of rock.
  • To a geologist, a rock's texture is the look and feel of the rock's top or surface.
    • Some are smooth and glassy.
    • Some are rough and chalky.
  • Lots or most rocks are made of particles of other minerals or other rocks, which gives a rock its texture.
• Grain Size
  • Lots of times, the grains in a rock are very big and easy to see or look at.
    • These rocks are called" coarse-grained"
  • Some other rocks, the grains can only be seen with a microscope.
    • These rocks are called " fine-grained".
• Grain Shape
  • The grains in a rock vary widley in shape.
    • Some grains look like very litttle pieces of sand.
    • Some others might look like seeds or some kind of exoloding star.
      • In some rocks, like granite, the grain results from the shape of the crystals that form that rock.
      • In some other rocks, the grain shape results from fragments of other rocks.
• Grain Pattern
  • The grains in a rock often form some kind of pattern.
  • Some rocks look like grains that looks like lots of rows of multicolored beads.
• No Visible Grain
  • Some rocks have no grain, even when they are examined under any microscope.
    • These rocks have no grain because when they form from magma or something, they cool very quickly.

Mineral Composition

• Lots of times, geologists have to look more closely at a rock than usual to determine its mineral composition.
  • By looking a a tiny silver of a rock under a microscope, a geologist can observe any rock's shape and size of crystals in the rock.
    • In identifying rocks, geologists also use some of the tests that are used to identify minerals.

Origin

• There are threee major groups of rocks.
  • Igneous rock
    • It forms from the cooling of molten rock either using magma below the surface or lava at the surface or top.
  • Sedimentary Rock
    • It forms when particles of other kinds of rock or the remains of plants of amimals are pressed and cemented together
      • Sedimentary rocks forms in layers under or below the surface.
  • Metamorphic Rock
    • It is formed when a rock that is already existing or there is changed by temperature, pressure, or chemical reactions.
      • Most metamorphic rock forms very deep underground.

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